1. Field of the Invention
The present invention relates to an apparatus for converting vector data representative of the outline of input characters such as alphabetic letters, Chinese characters, numberals and symbols, into corresponding dot data. More particularly, the present invention is concerned with a technique useful for reducing the time required for preparing dot data representative of characters.
2. Discussion of the Prior Art
For printing, displaying or otherwise reproducing or outputting input characters on an output medium such as a paper and a display screen, it is commonly practiced to prepare a batch of dot data consisting of bits indicative of the presence or absence of image dots to be formed at the positions of picture elements, which are the smallest subdivisions of an image to be outputted. If an output device such as a printer is adapted to store multiple sets of dot data representative of all characters that can be outputted on the output medium, the output device requires a memory having a large capacity. In view of this requirement, a set of vector data which defines the outline of each character available on the output device is usually stored in a memory, and the vector data of each input character are converted into the corresponding set of dot data for outputting the input character.
A data converting apparatus capable of converting vector data into dot data as described above is commonly arranged such that the output mode in which the characters are outputted can be changed or selected as desired. For instance, the characters can be printed or displayed in a selected one of different sizes (for example, 12-point or 20-point size), and/or in a selected one of different attitudes (for example, upright attitude and left-turned attitude as illustrated in FIG. 5). Further, the characters may have different type styles. For example, a character can be outputted in either the standard style in which the characters extend along their width-wise centerline, or in the italic style in which the characters are inclined with respect to the centerline, as indicated in FIG. 5. Thus, the characters are outputted in the specified mode in terms of one or more output conditions such as the character size, printing attitude and type style. Accordingly, the data converting apparatus should be adapted to be able to convert the vector data of each input character into corresponding dot data, so that the obtained dot data meet or satisfy the specified output mode, which may be a combination of two or more output conditions. For example, a set of dot data must be prepared so that the character is printed in the 10-point size, in the standard style and in the upright attitude.
Generally, a text to be outputted includes two or more occurrences of same characters. In this case, therefore, the conversion of the vector data into the dot data is effected two or more times for the same character which appears at two or more positions of the text. Since the data conversion requires a considerably long time, the repetition of the data converting operations for the same character results in unnecessarily increasing the overall time required to prepare a batch of dot data of the entire text. This waste of the data processing time may be avoided if the data converting apparatus is constructed to include: (a) V/D conversion means for converting vector data of an input character into dot data for reproducing or outputting the input character in a specified output mode on an output medium; (b) dot data memory means for storing the dot data prepared by the V/D conversion means; and (c) conversion control means operable prior to the data conversion by the V/D conversion means, for determining whether or not the dot data to be prepared by conversion from the vector data of the input character by the V/D conversion means are currently stored in the dot data memory, and activating the V/D conversion means to convert the vector data into the dot data if the dot data are not stored in the dot data memory, while omitting or inhibiting the conversion by the V/D conversion means if the dot data are stored in the memory.
In the known data converting apparatus indicated above, the dot data to be prepared by the V/D conversion means by conversion of the vector data of the input character permit the input character to be outputted in the specified output mode, namely, represent the kind of the input character, and reflect the specified output condition or conditions such as the character size, attitude and type style. The conversion of the vector data into the dot data is not effected where the dot data memory has already stored dot data identical with the dot data of the input character to be prepared by the V/D conversion means. In other words, the data conversion is effected only when the dot data for outputting the input character in the specified mode have not been stored in the dot data memory. Accordingly, the data conversion will not be repeated for preparing the dot data for outputting the same character in the same output mode, whereby the time for preparing the dot data for the input characters is considerably reduced.
However, an applicant's study on this type of data converting apparatus revealed a room for a further improvement in the apparatus. The applicant found it possible to omit the conversion of the vector data into the dot data even where dot data for outputting the same character as the input character in a mode different from the output mode of the input character are stored in the dot data memory, that is, even where the output mode of the input character is different from that of the dot data stored in the dot data memory for the same character.